1. Field of the Invention
The present invention relates to radiation detectors that produce large-area radiographic images by arranging a plurality of photoelectric conversion substrates.
2. Description of the Related Art
Planer x-ray detectors, which convert an x-ray image transmitted through a human body or the like into an electric signal, have become practical for use as medical x-ray diagnostic equipment. Most x-ray detectors that are used presently comprise: a photoelectric conversion substrate in which a light receiving part is formed from a substrate and a plurality of photoelectric conversion elements, such as photodiodes, arranged on the substrate two-dimensionally; and a scintillator layer formed on the light receiving part of the photoelectric conversion substrate. Such x-ray detectors convert x-rays transmitted through a human body or the like into visible light by means of the scintillator layer, convert the visible light into an electric signal by means of the photoelectric conversion elements of the photoelectric conversion substrate, and output this electric signal. In the photoelectric conversion substrate, a circuit board is formed from thin film transistors (TFT) arranged two-dimensionally, and the photoelectric conversion elements electrically connected to the thin film transistors are two-dimensionally arranged on this circuit board.
Radiographing a chest region (for example) requires a large-area x-ray detector. However, the larger the area becomes, the lower the yield becomes in the manufacture of photoelectric conversion substrates, and a larger manufacturing device and hence higher manufacturing cost are required for the photoelectric conversion substrates.
To overcome the foregoing problems, photoelectric conversion elements the area of each of which is smaller than the entire light receiving area of the x-ray detector are used, and the photoelectric conversion substrates are arranged to acquire a larger area. This prevents a decrease in yield per photoelectric conversion substrate and reduces the manufacturing cost.
However, where a large area is acquired by arranging a plurality of photoelectric conversion substrates, and scintillator layers are formed on the plurality of photoelectric conversion substrates, resolution diminishes in the boundaries (i.e., joints) between the adjacent photoelectric conversion substrates. To avoid this, all the photoelectric conversion substrates, including boundaries between one another, are covered with a transparent film in order to form a flat surface, and a scintillator layer is formed on this transparent film (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-48872, page 3 and FIG. 3).